As the electronics industry advances, and production of light weight components increases, the development of new materials gives producers increased options for further improving the performance and ease of manufacture of such components. Adhesive compositions, particularly conductive adhesives, are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses include bonding of electronic elements such as integrated circuit chips to lead frames or other substrates, and bonding of circuit packages or assemblies to printed wire boards.
Adhesives used in the electronic packaging industry typically contain a thermosetting resin combined with a filler and some type of curing initiator. These resins are primarily used in the electronics industry for the preparation of non-hermetic electronic packages. Adhesives useful for electronic packaging applications typically exhibit properties such as good mechanical strength, curing properties that do not affect the component or the carrier, and rheological properties compatible with application to microelectronic and semiconductor components. Examples of such packages are ball grid array (BGA) assemblies, super ball grid arrays, IC memory cards, chip carriers, hybrid circuits, chip-on-board, multi-chip modules, pin grid arrays, and the like.
For all these applications, the microelectronics industry continues to require new resins that are able to meet its varying demands. Accordingly, there is a need for the development of materials to address the requirements of this rapidly evolving industry.
An even broader need is for high performance matrix resins and adhesives for use in high performance applications. These applications include temperature resistant adhesives and components for use in automobile engine compartments, brake pads, aerospace re-entry vehicles, engine nacelles, kilns and boilers, etc. Other applications include those where a combination of high modulus and toughness are required such as in sail boat masts, golf clubs, tennis rackets, and airplane parts.
Bismaleimides have been an attractive class of thermoset resins because of their unique performance advantages. Bismaleimides can be cured via a variety of mechanisms. Homo-cures of bismaleimides produce polysuccinimide thermosets. These cross-linked polysuccinimides generally yield high glass transition temperature thermosets with excellent heat resistance and stiffness. However, the homo-cured bismaleimide resins are also noted for their extreme brittleness. One useful approach that has been used to improve the fracture toughness of bismaleimide thermosets has been to co-cure them with diene or polyene compounds via “ene” and/or Diels/Alder reactions. These co-cures can result in thermosets that retain the high thermal performance advantages of the original polysuccinimides while also providing a substantial improvement in fracture toughness.
The commercially available “ene” and/or Diels-Alder curatives for bismalemides include a variety of allyl and propenyl functional compounds. Examples of these compounds are shown below as C-1 through C-9. The most attractive curatives are those that can participate in both “ene” and Diels-Alder reactions (i.e. compounds C-1 through C-5). The C-6 through C-9 bismaleimide curatives, even though they generally co-cure with bismaleimides via the ene reaction alone, can be used at low levels as reactive diluents.
All of the commercial allyl and propenyl curatives react with bismalemides in one or more steps to yield thermoset resins. These reactions must generally be conducted at temperatures well above 200° C., and often over several hours. Furthermore, all of the dual reactive curatives (i.e. C-1 through C-5) are extremely viscous liquids or solids. The relatively low viscosity reactive diluents may be added, but their use is restricted by their inability to participate in both the “ene” and Diels-Alder reactions. Thus, the addition of significant levels of compounds C-6 through C-9 would degrade the performance of the final thermosets. There remains, therefore, a need for improved curatives for bismaleimide monomers.
